Driving device of motors for rolling rolls

ABSTRACT

A driving device driving motors of rolling rolls that corrects asymmetry between top and bottom roll driving systems of a twin-drive rolling mill in which top and bottom rolling rolls are driven by upper and lower motors, respectively, so that torques propagate to the top and bottom rolling rolls simultaneously. To this end, an upper/lower axis system imbalance correction section that corrects inequalities of torques propagating to the top and bottom rolling rolls is provided in either one or both of an upper motor control section that controls the upper motor and a lower motor control section that controls the lower motor in a driving device of motors for rolling rolls used in a rolling mill. The top and bottom rolling rolls are driven by the upper motor and the lower motor, respectively, and one of the upper motor and the lower motor is located on a rolled material. Thus, torques propagate to the top and bottom rolling rolls simultaneously.

TECHNICAL FIELD

The present invention relates to a driving device of motors for rollingrolls and, more particularly, to a driving device of motors for rollingrolls that is used in a twin-drive type rolling mill in which top andbottom rolling rolls are driven by separate motors.

BACKGROUND ART

In a twin-drive type rolling mill in which top and bottom rolling rollsare driven by an upper motor and a lower motor, respectively, each ofthe motors is controlled by an independent control system. Therefore,loads of the upper and lower motors become nonuniform and thermalimbalance of the motors and bows in a rolled material caused bydifferences in upper and lower torques may occur. Therefore, to make theloads of the upper and lower motors uniform and to prevent upward bowsand downward bows of a rolled material, there is known a load balancecontrol method that involves monitoring standard values or measuredvalues of load currents of the upper and lower motors and making thestandard values or the measured values uniform (refer to Patent Document1, for example).

A motor for rolling has mechanical loads of a multiple mass point springsystem composed of spindles, couplings, rolls, gears and the like. Whenthe natural frequency of a rolling roll driving system including motorsand the speed response frequency of a speed controller of motors forrolling become close to each other, the rolling mill driving systemincluding a control system and a mechanical system becomes an unstablesystem due to the resonance of the two and the phenomenon of excessivetorsional vibration may occur.

To cope with such torsional vibration, it is general practice toevaluate the natural frequency of each of the top and bottom roll axissystems in the design stage and to design the speed response frequencyand natural frequency to provide sufficiently different values so as toavoid the resonance phenomenon. Also, there is known a technique thatinvolves incorporating a model of a mechanical system in a controlsystem, estimating the behavior of the mechanical system, and correctinga torque standard, whereby vibration is suppressed (refer to PatentDocument 2, for example).

Patent Document 1: Japanese Patent Laid-Open No. 09-295016

Patent Document 2: Japanese Patent Laid-Open No. 06-98580

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

In a twin-drive type rolling mill in which top and bottom rolling rollsare driven by an upper motor and a lower motor, respectively, as isapparent from the schematic configuration of the twin-drive type rollingmill shown in FIG. 5, due to problems of the lubrication of universalcouplings 54, 55, 56, 57 that connect a top rolling roll 50 and an uppermotor 51 together and a bottom rolling roll 52 and a lower motor 53together and the like, it is impossible to increase the inclinationangles of spindles 58, 59 between the universal couplings 54 and 55 orbetween the universal couplings 56 and 57. Therefore, the gap betweenthe upper and lower motors 51, 53 is reduced by arranging either theupper motor 51 or the lower motor 53 more forward, that is, toward therolled material 60 side compared to the other, whereby it is necessaryto reduce the inclination angles of the spindles 58, 59. Inconsideration of the foregoing, arranging the upper motor 51 moreforward than the lower motor 53 is referred to as the top forwardmethod, and arranging the lower motor 53 more forward than the uppermotor 51 is referred to as the bottom forward method.

FIG. 5 shows the schematic configuration of a rolling roll drivingsystem of the top forward method in which the upper motor 51 is arrangedmore forward than the lower motor 53. As shown in this drawing, in atwin-drive type rolling mill, the mechanical makeup of the upper andlower driving axis systems does not become identical and the two havedifferent transfer functions. For this reason, as in the control methodof motors for rolling rolls disclosed in Patent Document 1, the torquesthat propagate to the top surface and bottom surface of a rolledmaterial 60 become transiently unequal even when the motor outputtorques are controlled to be identical for the upper and lower drivingaxis systems and this may cause bows in the rolled material 60 or damagethereto, for example. Incidentally, reference numerals 61, 62 of FIG. 5denote backup rolls that back up the top rolling roll 50 and the bottomrolling roll 52, respectively, and reference numeral 63 denotes aconnection between the lower motor 53 and the universal coupling 57.

In load balance control that has been used to eliminate thenonuniformity of upper and lower torques in a twin-drive type rollingmill, upper and lower torques (load currents) in motors are monitoredand made uniform, and no consideration is given to the inequalities ofupper and lower torques that occur when the torques propagate to therolling rolls from the motors.

The technique of incorporating a model of a mechanical system in acontrol system, which is disclosed in Patent Document 2, is used intorsional vibration suppression and control and the like as describedabove. However, in the monitoring and controlling of the behavior ofupper and lower mechanical axis systems, this technique is apt to bedirectly affected by modeling errors. Furthermore, models of both ofupper and lower mechanical systems and control feedback values are alsonecessary, and the control system becomes complicated.

The present invention has been made to solve problems as describedabove, and provides a driving device of motors for rolling rolls thatcorrects inequalities of torques propagating to top and bottom rollingrolls of a twin-drive type rolling mill and accomplishes the synchronismof torque transmission to the top and bottom rolling rolls.

Means for Solving the Problems

A driving device of motors for rolling rolls used in a rolling mill inwhich top and bottom rolling rolls are driven by an upper motor and alower motor, respectively, and either the upper motor or the lower motoris arranged to a rolled material side compared to the other motor, ischaracterized in that either one or both of an upper motor controlsection that controls the upper motor and a lower motor control sectionthat controls the lower motor are provided with an upper/lower axissystem imbalance correction section that corrects inequalities oftorques propagating to the top and bottom rolling rolls.

ADVANTAGES OF THE INVENTION

According to the present invention, it is possible to make equal thetransfer functions of the driving systems of the top and bottom rollingrolls including control systems and mechanical systems and to accomplishthe synchronism of torque transmission to the top and bottom rollingrolls. Therefore, it is possible to make equal torques propagating tothe top surface and bottom surface of a rolled material, and thiseliminates the possibility of causing bows in a rolled materials ordamage thereto.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic control block diagram showing a driving device ofmotors for rolling rolls related to Embodiment 1 of the presentinvention.

FIG. 2 is a schematic control block diagram showing a driving device ofmotors for rolling rolls related to Embodiment 2 of the presentinvention.

FIG. 3 is a schematic control block diagram showing a driving device ofmotors for rolling rolls related to Embodiment 3 of the presentinvention.

FIG. 4 is a schematic control block diagram of the load balancecalculation section.

FIG. 5 is a schematic control block diagram showing a prior drivingdevice of motors for rolling rolls.

FIG. 6 shows simulated waveforms of torques propagating to the top andbottom rolling rolls without a correction.

FIG. 7 shows the gain characteristics of the top and bottom roll axissystems without a correction.

FIG. 8 is a block diagram of a roll axis system represented by a masspoints system (the number of mass points is set equal to n).

FIG. 9 is a block diagram of a roll axis system approximated by atwo-mass point system.

FIG. 10 shows simulated waveforms of torques propagating to the top andbottom rolling rolls with a correction.

FIG. 11 shows the gain characteristics of the top and bottom roll axissystems with a correction.

DESCRIPTION OF SYMBOLS

-   -   1 upper motor control section    -   2 upper motor speed controller    -   3 upper motor torque current limiter    -   4 upper motor current controller    -   5,51 upper motor    -   6 upper motor speed sensor    -   7 upper motor torque control means    -   8 lower motor control section    -   9 lower motor speed controller    -   10 lower motor torque current limiter    -   11 lower motor current controller    -   12,53 lower motor    -   13 lower motor speed sensor    -   14 lower motor torque control means    -   15 top roll axis system    -   16 bottom roll axis system    -   17 upper motor speed standard section    -   18 lower motor speed standard section    -   19 upper/lower axis system imbalance correction section    -   20,60 rolled material    -   21 top roll driving system    -   22 bottom roll driving system    -   30 load balance calculation section    -   50 top rolling roll    -   52 bottom rolling roll    -   58,59 spindle    -   54,55,56,57 universal coupling    -   61,62 backup roll    -   63 connection

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to the accompanying drawings, a description will be givenbelow of preferred embodiments of a driving device of motors for rollingrolls related to the present invention.

Embodiment 1

Embodiment 1 of the present invention will be described on the basis ofFIG. 1. FIG. 1 is a schematic control block diagram showing a drivingdevice of motors for rolling rolls related to Embodiment 1 of thepresent invention, and shows an embodiment of the top forward method inwhich an upper motor is arranged more forward than a lower motor.

In FIG. 1, an upper motor control section 1 is composed of an uppermotor speed controller 2, an upper motor torque current limiter 3, andan upper motor current controller 4. An upper motor 5 is controlled bythis upper motor control section 1, and the rotation speed thereof isdetected by an upper motor speed sensor 6. Incidentally, as will bedescribed later, the upper motor torque current limiter 3 and the uppermotor current controller 4 constitute upper motor torque control means 7that controls the torque of the upper motor 5 so that a deviation of anactual speed of the upper motor from a speed standard for the uppermotor becomes zero.

A lower motor control section 8 is composed of a lower motor speedcontroller 9, a lower motor torque current limiter 10, and a lower motorcurrent controller 11. A lower motor 12 is controlled by this lowermotor control section 8, and the rotation speed thereof is detected by alower motor speed sensor 13. Incidentally, as will be described later,the lower motor torque current limiter 10 and the lower motor currentcontroller 11 constitute lower motor torque control means 14 thatcontrols the torque of the lower motor 12 so that a deviation of anactual speed of the lower motor from a speed standard for the lowermotor becomes zero. Reference numeral 15 denotes a top roll axis systemextending from the upper motor 5 to a top rolling roll (not shown), andreference numeral 16 denotes a bottom roll axis system extending fromthe lower motor 12 to a bottom rolling roll (not shown).

There is provided an upper motor speed standard section 17 that issuescommands for the speed standard for the upper motor 5 to the upper motorcontrol section 1, and there is provided a lower motor speed standardsection 18 that issues commands for the speed standard for the lowermotor 12 to the lower motor control section 8. Furthermore, anupper/lower axis system imbalance correction section 19 that performsoperations described below is provided in the rear of the upper motorspeed standard section 17.

As described above, the upper motor 5 and the lower motor 12 are eachcontrolled by the motor control sections 1, 8 that are independent ofeach other, and output torques of each of the motors 5, 12 propagatethrough the top roll axis system 15 and the bottom roll axis system 16,respectively, and reach a rolled material 20. As a result of this, therolled material 20 is rolled. Incidentally, the upper/lower axis systemimbalance correction section 19, the upper motor control section 1, theupper motor 5, the upper motor speed sensor 6, and the top roll axissystem 15 constitute a top roll driving system 21, and the lower motorcontrol section 8, the lower motor 12, the lower motor speed sensor 13,and the bottom roll axis system 16 constitute a bottom roll drivingsystem 22.

The driving device of motors for rolling rolls related to the Embodiment1 is constructed as described above, and the operation thereof will bedescribed next.

First, in the top roll driving system 21, an upper motor torque currentstandard TA is obtained by inputting to the upper motor speed controller2 a deviation of an actual speed SP3 of the upper motor 5 detected bythe upper motor speed sensor 6 from a corrected speed standard SP2obtained by inputting a speed standard SP1 from the upper motor speedstandard section 17 to the upper/lower axis system imbalance correctionsection 19. Furthermore, power is supplied to the upper motor 5 via theupper motor torque current limiter 3 and the upper motor currentcontroller 4. As a result of this, the torque of the upper motor 5 iscontrolled so that a deviation of the actual speed SP3 of the uppermotor 5 from the upper motor speed standard SP1 becomes zero.

On the other hand, in the bottom roll driving system 22, a lower motortorque current standard TB is obtained by inputting to the lower motorspeed controller 9 a deviation of an actual speed SP5 of the lower motor12 detected by the lower motor speed sensor 13 from a speed standard SP4from the lower motor speed standard section 18. Furthermore, power issupplied to the lower motor 12 via the lower motor torque currentlimiter 10 and the lower motor current controller 11. As a result ofthis, the torque of the lower motor 12 is controlled so that a deviationof the actual speed SP5 of the lower motor 12 from the lower motor speedstandard SP4 becomes zero.

Torques supplied from the upper motor 5 and the lower motor 12 arecaused to propagate to the top surface and bottom surface of the rolledmaterial 20 via the top roll axis system 15 and the bottom roll axissystem 16, respectively. As described in the conventional art, thetransfer function G_(T)(s) of the top roll axis system 15 and thetransfer function G_(B)(s) of the bottom roll axis system 16 do notbecome identical due to mechanical restrictions of a twin-drive typerolling mill. The torques that propagate to the top surface and bottomsurface of the rolled material 20 become transiently unequal even whenthe torques supplied from the upper motor 5 and the lower motor 12 arecontrolled to be identical and this may cause bows in the rolledmaterial 20 or damage thereto, for example. To eliminate this, in thisembodiment, the transfer function C₁(s) is set as given byC₁(s)=G_(B)(s)/G_(T)(s) in the upper/lower axis system imbalancecorrection section 19 for the purpose of accomplishing the synchronismof torque transmission to the top and bottom rolling rolls. As a resultof this, it becomes possible to ensure that the top roll driving system21 comprising the upper/lower axis system imbalance correction section19, the upper motor control section 1, the upper motor 5, the uppermotor speed sensor 6, and the top roll axis system 15 and the bottomroll driving system 22 comprising the lower motor control section 8, thelower motor 12, the lower motor speed sensor 13, and the bottom rollaxis system 16 have the same transfer function, and it is possible toeliminate the inequalities of upper and lower torques caused to betransmitted to the rolled material 20.

As described above, according to Embodiment 1, it is possible toaccomplish the synchronism of torque transmission to the top and bottomrolling rolls. Therefore, it is possible to make the torques propagatingto the top surface and bottom surface of the rolled material 20identical to each other, and this eliminates the possibility of causingbows in the rolled material 20 or damage thereto.

Embodiment 2

Next, Embodiment 2 of the present invention will be described. InEmbodiment 1, the description was given of the embodiment in which theupper/lower axis system imbalance correction section 19 is arranged inthe rear of the upper motor speed standard SP1. However, by providingthis correction section 19 within a speed control loop, it is possibleto cause the correction section 19 to approach the machine side and,therefore, it is possible to further increase the effect of thecorrection of inequalities of torques propagating to the top and bottomrolling rolls.

FIG. 2 is a schematic control block diagram showing a driving device ofmotors for rolling rolls related to Embodiment 2. As is apparent fromthis drawing, an upper/lower axis system imbalance correction section 19is provided in the rear of a speed controller 2, which is within anupper motor speed feedback loop. Furthermore the transfer function ofthe upper/lower axis system imbalance correction section 19 is set asgiven by C₂(s)=C₁(s)/{1+G_(L)(s)}{1−C₁(s)}. In this equation, G_(L)(s)is the open-loop transfer function of a speed feedback loop inEmbodiment 1. That is, because in Embodiment 1 the upper/lower axissystem imbalance correction section 19 is installed in front of theupper motor speed feedback loop, the transfer function is set as givenby C₁(s)=G_(B)(s)/G_(T)(s). In Embodiment 2, however, because thecorrection section 19 is installed within the upper motor speed feedbackloop, the transfer function is set as given byC₂(s)=C₁(s)/{1+G_(L)(s)}{1−C₁(s)}. Incidentally, because Embodiment 2 isthe same as Embodiment 1 in other constituent features, the descriptionthereof is omitted.

According to Embodiment 2, the effects of Embodiment 1 are produced andit is possible to cause the upper/lower axis system imbalance correctionsection 19 to approach the machine side. Therefore, it is possible tofurther increase the effect of the correction of inequalities of torquespropagating to the top and bottom rolling rolls.

Embodiment 3

Next, Embodiment 3 of the present invention will be described. InEmbodiment 3, the synchronism of torque transmission to the top andbottom rolling rolls is increased by using the upper/lower axis systemimbalance correction section 19 of Embodiment 2 in combination with loadbalance control.

FIG. 3 is a schematic control block diagram showing a driving device ofmotors for rolling rolls related to Embodiment 3. The driving device ofmotors for rolling rolls related to Embodiment 3 quickly corrects animbalance of the torque current standards TA and TB for the upper motor5 and the lower motor 12, respectively, by inputting the upper and lowermotor torque current standards to a load balance calculation section 30and directly adding correction amounts to the upper torque currentstandard. Incidentally, because Embodiment 3 is the same as Embodiment 2in other constituent features, the description thereof is omitted.

FIG. 4 shows a schematic control block diagram of the load balancecalculation section 30. Corrections are performed by multiplying adeviation of the upper and lower torque current standards TA and TB by aload balance calculation limiter 30 a and a load balance calculationrate 30 b, performing proportional control 30 c, and performing anaddition to the current standard TA for the upper motor 5. Furthermore,as shown in FIG. 3, by arranging the upper/lower axis system imbalancecorrection section 19 in the rear of the load balance calculationsection 30, it becomes possible to further increase the synchronism oftorque transmission to the top and bottom rolling rolls.

As described above, according to Embodiment 3, it becomes possible toobtain the synchronism of torque transmission to the top and bottomrolling rolls, with the effect obtained by Embodiment 1 or Embodiment 2further increased.

This embodiment is more effective when a correction term, which will bedescribed later in Embodiment 4, is used in a simplified manner.

Embodiment 4

Next, Embodiment 4 of the present invention will be described. InEmbodiment 4, the top and bottom roll axis systems in Embodiments 1 to 3are approximated by spring and mass systems, whereby the transferfunction of a correction term in an upper/lower axis system imbalancecorrection section 19 is expressed by physical parameters of the springand mass systems.

FIG. 6 shows examples of a simulation of torque waveforms at top andbottom rolling roll ends and a waveform of upper and lower torquedifference that are obtained when external forces corresponding to ratedtorques of the motors are applied in a stepped manner to the motors androlling roll ends of a twin-drive type rolling mill, that is, during theentry of a material into the rolls. In this example, the top roll axissystem and the bottom roll axis system are approximated by a four-masspoint spring and mass system and a five-mass point spring and masssystem, respectively, and the primary natural torsional frequency of thetop roll axis system and the bottom roll axis system is approximately13.6 Hz and approximately 11.8 Hz, respectively. An imbalance occursgradually in the torques transmitted to the top and bottom rolling rollsafter a point in time of 0.2 second when the stepped load is applied anda torque difference that is as great as 0.8 PU maximum (the rated torquestandard for the motors) occurs via the rolled material. It is apparentthat the main components of vibrations are primary torsional frequenciesof the top and bottom rolling rolls. FIG. 7 shows the gaincharacteristics of the top and bottom roll axis systems and a differencein the gains between the top and bottom roll axis systems (20log(G_(B)(s)/G_(T)(s))). By providing an imbalance correction term thatcompensates for this gain difference between the top and bottom axissystems in either one or both of the upper motor control system and thelower motor control system, it is possible to eliminate inequalities ofupper and lower torques.

The spring and mass systems used as the transfer functions of the topand bottom roll axis systems in a correction term can approximate amechanical axis system by increasing the number of mass points of theaxis system model. However, when a correction term is actually appliedto a control system, the order of a transfer function is increased by anincrease in the number of mass points and the transfer function becomesvery complex, with the result that increasing the number of mass pointslacks feasibility in terms of restrictions on the sampling intervals inthe control system and that the number of adjusting parameters of thecorrection term also increases. FIG. 8 shows for reference a blockdiagram of a roll axis system obtained when the number of mass points isset equal to n.

Because a certain level of torque difference poses no problem in actualoperation and it is unnecessary to completely eliminate inequalities ofupper and lower torques, it is possible to simplify a correction term byreducing the number of mass points. In this embodiment, the dimension ofa correction term is made low by approximating the top and bottom rollaxis systems each by a two-mass point system, making the application ofa correction term to the existing control system sufficiently possibleand reducing the imbalance of the upper and lower torques due to themost remarkable primary torsional frequency. FIG. 9 shows a blockdiagram of a roll axis system approximated by a two-mass point system.From FIG. 9, the transfer function of torques from a motor to a roll endin the case where a roll axis system is approximated by a two-mass pointsystem becomes as given by:

$\begin{matrix}{{G(s)} = \frac{{J_{2} \cdot C \cdot s} + {J_{2} \cdot K}}{{J_{1} \cdot J_{2} \cdot s^{2}} + {\left( {J_{1} + J_{2}} \right) \cdot C \cdot s} + {\left( {J_{1} + J_{2}} \right) \cdot K}}} & \left\lbrack {{Expression}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Therefore, from the transfer function simplified to the two-mass pointsystem given in expression 1, the transfer function of the correctionterm is found as given by:

$\begin{matrix}\begin{matrix}{{C_{1}(s)} = {{G_{B}(s)}/{G_{T}(s)}}} \\{= {\frac{{J_{B\; 2} \cdot C_{B} \cdot s} + {J_{B\; 2} \cdot K_{B}}}{{J_{B\; 1} \cdot J_{B\; 2} \cdot s^{2}} + {\left( {J_{B\; 1} + J_{B\; 2}} \right) \cdot C_{B} \cdot s} + {\left( {J_{B\; 1} + J_{B\; 2}} \right) \cdot K_{B}}} \times}} \\{{\frac{{J_{T\; 1} \cdot J_{T\; 2} \cdot s^{2}} + {\left( {J_{T\; 1} + J_{T\; 2}} \right) \cdot C_{T} \cdot s} + {\left( {J_{T\; 1} + J_{T\; 2}} \right) \cdot K_{T}}}{{J_{T\; 2} \cdot C_{T} \cdot s} + {J_{T\; 2} \cdot K_{T}}} \times}} \\{A_{com}}\end{matrix} & \left\lbrack {{Expression}\mspace{14mu} 2} \right\rbrack\end{matrix}$

where, J_(T1), J_(T2) are the motor-side and roll-side inertia of thetop roll axis system, K_(T) is the spring constant of the top roll axissystem, C_(T) is the attenuation coefficient of the top roll axissystem, J_(B1) J_(B2) are the motor-side and roll-side inertia of thebottom roll axis system, K_(B) is the spring constant of the bottom rollaxis system, and C_(B) is the attenuation coefficient of the bottom rollaxis system. These coefficients are all adjustable. A_(com) is acorrection coefficient to make the deviation of the correction termzero, and is expressed by the following expression.

$\begin{matrix}{A_{com} = \frac{J_{T\; 2} \cdot \left( {J_{B\; 1} + J_{B\; 2}} \right)}{J_{B\; 2} \cdot \left( {J_{T\; 1} + J_{T\; 2}} \right)}} & \left\lbrack {{Expression}\mspace{14mu} 3} \right\rbrack\end{matrix}$

Results of a simulation of torque waveforms at top and bottom rollingroll ends and a waveform of upper and lower torque difference obtainedwhen expression 2 is inserted into the top roll axis system as acorrection term are shown in FIG. 10, and the gain characteristics ofthe top roll axis system including the correction term, the bottom rollaxis system, and the correction term are shown in FIG. 11. It isapparent that due to the imbalance correction term, it has becomepossible to make the primary torsional frequency of the top roll axissystem almost equal to that of the bottom roll axis system, with theresult that it has become possible to make the maximum value of a torquedifference in the top and bottom rolling rolls to 0.3 PU. That is, theresults show that the effect of the correction is sufficient even whenthe top and bottom roll axis systems are approximated by a two-masspoint system. A correction term is calculated beforehand in this mannerand the fine tuning of each of the above-described parameters isperformed during the installation and adjustment of actual equipment,whereby it is possible to expect a higher-accuracy correction.Techniques for adjusting each of the parameters by the actualmeasurement of torques transmitted to roll ends by use of strain gaugesand the actual measurement of a transfer function by use of a transferfunction measuring device are conceivable as methods of on-siteadjustment of a correction term.

As described above, according to Embodiment 4, the effects obtained inEmbodiments 1 to 3 are produced and it is possible to further increasethe effect of the correction of inequalities of torques propagating tothe top and bottom rolling rolls by performing prior evaluation andverification of the effect of the correction of a correction term by atransfer function by a simulation.

Incidentally, in Embodiment 1 the description was given of theembodiment in which the upper/lower axis system imbalance correctionsection 19 is arranged in the rear of the upper motor speed standard SP1and in Embodiment 2 the description was given of the embodiment in whichthe upper/lower axis system imbalance correction section 19 is arrangedwithin the upper motor speed feedback loop. In the present invention,however, the upper/lower axis system imbalance correction section 19 maybe arranged in the same position as described above in the bottom rolldriving system 22, and may also be arranged in the same position asdescribed above in both of the top roll driving system 21 and the bottomroll driving system 22. Furthermore, in each of the above-describedembodiments, the graphical description was given of the embodiments inwhich the present invention is applied to the driving device of motorsfor rolling rolls in a top forward type rolling mill. However, thepresent invention may also be applied to a driving device of motors forrolling rolls in a bottom forward type rolling mill and hence thepresent invention includes various kinds of design changes.

INDUSTRIAL APPLICABILITY

The present invention can be applied to a driving device of motors forrolling rolls in a twin-drive type rolling mill in which the top andbottom rolling rolls are driven by separate motors.

1. A driving device driving motors of rolling rolls in a rolling mill in which top and bottom rolling rolls are driven by an upper motor and a lower motor, respectively, and one of the upper motor and the lower motor is located on a rolled material side, as compared to the other motor, comprising: an upper motor control section that controls the upper motor, and a lower motor control section that controls the lower motor, wherein at least one of the upper control section and the lower control section includes an upper/lower axis system imbalance correction section that corrects inequalities of torques propagating to the top and bottom rolling rolls.
 2. The driving device driving motors of rolling rolls according to claim 1, wherein the upper motor control section comprises an upper motor speed controller that receives, as an input, deviation of actual speed of the upper motor from a speed standard for the upper motor and obtains a torque standard for the upper motor, and upper motor torque control means that controls torque of the upper motor so that the deviation of the actual speed of the upper motor from the speed standard for the upper motor becomes zero, the lower motor control section comprises a lower motor speed controller that receives, as an input, deviation of actual speed of the lower motor from a speed standard for the lower motor and obtains a torque standard for the lower motor, and lower motor torque control means that controls torque of the lower motor so that the deviation of the actual speed of the lower motor from the speed standard for the lower motor becomes zero, and the upper/lower axis system imbalance correction section precedes at least one of the upper motor control section and the lower motor control section.
 3. The driving device driving motors of rolling rolls according to claim 1, wherein the upper motor control section comprises an upper motor speed controller that receives, as an input, deviation of actual speed of the upper motor from a speed standard for the upper motor and obtains a torque standard for the upper motor, and upper motor torque control means that controls torque of the upper motor so that the deviation of the actual speed of the upper motor from the speed standard for the upper motor becomes zero, the lower motor control section comprises a lower motor speed controller that receives, as an input, deviation of actual speed of the lower motor from a speed standard for the lower motor and obtains a torque standard for the lower motor, and lower motor torque control means that controls torque of the lower motor so that the deviation of the actual speed of the lower motor from the speed standard for the lower motor becomes zero, and the upper/lower axis system imbalance correction section is within a speed control loop of at least one of the upper motor control section and the lower motor control section.
 4. The driving device driving motors of rolling rolls according to claim 1, further comprising a load balance calculation section that suppresses load imbalance of the upper and lower motors by adding an imbalance correction amount, calculated from torque current standards for the upper motor and the lower motor, directly to the torque current standards, wherein the load balance calculation section precedes the upper/lower axis system imbalance correction section.
 5. The driving device driving motors of rolling rolls according to claim 1, wherein the upper/lower axis system imbalance correction section corrects inequalities of torques propagating to the top and bottom rolling rolls by using physical parameters of a spring and mass system that approximately express a top roll axis system extending from the upper motor to the top rolling roll and a bottom roll axis system extending from the lower motor to the bottom rolling roll.
 6. The driving device driving motors of rolling rolls according to claim 5, wherein the spring and mass system that approximately expresses the top and bottom roll axis systems is a two-mass point system.
 7. The driving device driving motors of rolling rolls according to claim 2, further comprising a load balance calculation section that suppresses load imbalance of the upper and lower motors by adding an imbalance correction amount, calculated from torque current standards for the upper motor and the lower motor, directly to the torque current standards, wherein the load balance calculation section precedes the upper/lower axis system imbalance correction section.
 8. The driving device driving motors of rolling rolls according to claim 3, wherein the driving device further comprises a load balance calculation section that suppresses load imbalance of the upper and lower motors by adding an imbalance correction amount, calculated from torque current standards for the upper motor and the lower motor, directly to the torque current standards, wherein the load balance calculation section precedes in front of the upper/lower axis system imbalance correction section.
 9. The driving device driving motors of rolling rolls according to claim 2, wherein the upper/lower axis system imbalance correction section corrects inequalities of torques propagating to the top and bottom rolling rolls by using physical parameters of a spring and mass system that approximately express a top roll axis system extending from the upper motor to the top rolling roll and a bottom roll axis system extending from the lower motor to the bottom rolling roll.
 10. The driving device driving motors of rolling rolls according to claim 3, wherein the upper/lower axis system imbalance correction section corrects inequalities of torques propagating to the top and bottom rolling rolls by using physical parameters of a spring and mass system that approximately express a top roll axis system extending from the upper motor to the top rolling roll and a bottom roll axis system extending from the lower motor to the bottom rolling roll.
 11. The driving device driving motors of rolling rolls according to claim 4, wherein the upper/lower axis system imbalance correction section corrects inequalities of torques propagating to the top and bottom rolling rolls by using physical parameters of a spring and mass system that approximately express a top roll axis system extending from the upper motor to the top rolling roll and a bottom roll axis system extending from the lower motor to the bottom rolling roll.
 12. The driving device driving motors of rolling rolls according to claim 7, wherein the upper/lower axis system imbalance correction section corrects inequalities of torques propagating to the top and bottom rolling rolls by using physical parameters of a spring and mass system that approximately express a top roll axis system extending from the upper motor to the top rolling roll and a bottom roll axis system extending from the lower motor to the bottom rolling roll.
 13. The driving device driving motors of rolling rolls according to claim 8, wherein the upper/lower axis system imbalance correction section corrects inequalities of torques propagating to the top and bottom rolling rolls by using physical parameters of a spring and mass system that approximately express a top roll axis system extending from the upper motor to the top rolling roll and a bottom roll axis system extending from the lower motor to the bottom rolling roll.
 14. The driving device driving motors of rolling rolls according to claim 9, wherein the spring and mass system that approximately expresses the top and bottom roll axis systems is a two-mass point system.
 15. The driving device driving motors of rolling rolls according to claim 10, wherein the spring and mass system that approximately expresses the top and bottom roll axis systems is a two-mass point system.
 16. The driving device driving motors of rolling rolls according to claim 11, wherein the spring and mass system that approximately expresses the top and bottom roll axis systems is a two-mass point system.
 17. The driving device driving motors of rolling rolls according to claim 12, wherein the spring and mass system that approximately expresses the top and bottom roll axis systems is a two-mass point system.
 18. The driving device of driving motors for of rolling rolls according to claim 13, characterized in that the spring and mass system that approximately expresses the top and bottom roll axis systems is a two-mass point system. 